The Inhibitory Effects of Nitrogen Deposition on Asymbiotic Nitrogen Fixation are Divergent Between a Tropical and a Temperate Forest

et al. 2019

JGR Biogeosciences

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Evidence shows that nitrogen (N) addition may suppress or have no significant effect on asymbiotic N2 fixation (ANF) in soil, litter, or moss. However, the mechanisms underlying the differential responses of ANF to N addition are not well understood. The main objectives of the current study were to assess how ANF in soil, litter, and moss responds to N addition and whether topography modulates the responses of ANF in soil, litter, or moss to N addition. We conducted an N addition experiment at two topographic positions, that is, valley and slope of a secondary karst forest in southwest China. Three N addition treatments, that is, control (0 kg N·ha−1·year−1), moderate N addition (N50, 50 kg N·ha−1·year−1), and high N addition (N100, 100 kg N·ha−1·year−1) were included. Nitrogen addition had no significant effect on moss ANF at both topographic positions. Soil ANF was lower by 17.1% in the N100 plots relative to the control in the valley but was not significantly altered by N addition on the slope. In contrast, litter ANF was suppressed by N addition at both topographic positions by 77.9% to 87.4%. Our findings suggest that topography may modulate the responses of ANF to N addition, but the modulation effects likely differ among different ecosystem compartments.

Section: Responses Of Asymbioitic N 2 Fixation To N Additionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

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Topography Modulates Effects of Nitrogen Deposition on Asymbiotic N₂ Fixation in Soil but not Litter or Moss in a Secondary Karst Forest

Wang

et al. 2019

JGR Biogeosciences

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“…; Zheng et al . ). Fertilisers (NH 4 NO 3 ) mixed with 10 L and 20 L of water were sprayed below the canopy using a backpack sprayer in the N‐addition plots at the HS (bimonthly from August 2010 to July 2014) and DHS2 (monthly from July 2003 to July 2015) sites, respectively, and an equivalent volume of water was sprayed in control plots.…”

Section: Methodsmentioning

confidence: 97%

Substrate stoichiometry determines nitrogen fixation throughout succession in southern Chinese forests

Chen

et al. 2019

Ecology Letters

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The traditional view holds that biological nitrogen (N) fixation often peaks in early‐ or mid‐successional ecosystems and declines throughout succession based on the hypothesis that soil N richness and/or phosphorus (P) depletion become disadvantageous to N fixers. This view, however, fails to support the observation that N fixers can remain active in many old‐growth forests despite the presence of N‐rich and/or P‐limiting soils. Here, we found unexpected increases in N fixation rates in the soil, forest floor, and moss throughout three successional forests and along six age‐gradient forests in southern China. We further found that the variation in N fixation was controlled by substrate carbon(C) : N and C : (N : P) stoichiometry rather than by substrate N or P. Our findings highlight the utility of ecological stoichiometry in illuminating the mechanisms that couple forest succession and N cycling.

“…Most N addition experiments directly applied N to the soil or sprayed the understory (Högberg et al, 2006;Lu et al, 2010;Mao et al, 2018), overlooking the importance of canopy retention of N (Liu et al, 2018;Zhang et al, 2015). These findings highlight that canopy foliage plays an important role in retaining the deposited N and that many understory N addition experiments cannot reflect the true effects of atmospheric N deposition on ecological processes (including foliar retention of nutrients), as revealed by several recent studies (Zhang et al, 2015;Zheng et al, 2018).…”

Section: Journal Of Geophysical Research: Biogeosciencesmentioning

confidence: 99%

Responses of Foliar Nutrient Status and Stoichiometry to Nitrogen Addition in Different Ecosystems: A Meta‐analysis

Mao

2020

JGR Biogeosciences

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Atmospheric nitrogen (N) deposition alters the cycling of nutrients in terrestrial ecosystems. However, there is limited knowledge regarding how N addition affects foliar nutrients beyond N and phosphorus (P) and their stoichiometry. We conducted a meta‐analysis, including 2,004 observations from 134 fertilization studies, to synthesize the effects of N addition on multiple foliar nutrients and stoichiometry in terrestrial ecosystems and to examine their potential controls. Overall, we found that N addition significantly decreased foliar P, potassium (K), calcium (Ca), magnesium (Mg), and calcium:aluminium (Ca:Al) by 3.22%, 7.58%, 9.55%, 5.65%, and 15.17%, respectively, but significantly increased foliar N, Al, N:K, N:Ca, and N:Mg by 19.02%, 6.99%, 21.06%, 27.65%, and 11.33%, respectively. Among the forest ecosystems, foliar N and P exhibited greater changes in temperate or boreal forests, and foliar K, Mg, and Mn showed greater decreases or increases in tropical forests after N addition. Nitrogen addition significantly affected foliar K (−7.55%), Mg (−6.46%), and Al (+6.81%) in forests but not in grasslands. Similarly, foliar K, Mg, and Al showed significant changes in woody plants but not in herbaceous plants. In addition, we found that environmental factors (e.g., ambient N deposition, mean annual precipitation, and soil pH) affected foliar nutrient responses of N, K, and Mg to N addition. In summary, our findings indicate that N addition affects foliar nutrient contents, with the extent of these effects differing among ecosystem type. This is important for understanding and predicting plant growth and nutrient dynamics under N deposition scenarios.